Alignment - universal D&D axiology

I always use alignment rules in my D&D campaigns. How could I not? They're one of the fundaments of the multiverse, regardless of the setting. Leaving it out would deprive me of numerous plot and game options. What about Paladin's skills? Aligned magic items? Alignment based spells?

I carefully read the more interesting anti-alignment rants yet to me this is a very simple matter.
In terms of axiology we can either have absolute or relative values. Such values as 'Good' or 'Evil' can either be universal, imposed by a superior axiological system (through a omnipotent being perhaps) or relative if we assume that this axiological system is only one of many (the omnipotent being has peers with different ideas). So there is either an absolute 'Good', a fixed reference point on the universe, or a 'Good' that is good for me but may not be good for you (Kill all of them! God will know his flock.)

D&D ostensibly recognized absolute values and connects them with godly powers that roam the known Multiverse. There is 'Good' as a general respect and protection of life, there is 'Evil' as its direct opposition. We've got Law as an expression of the general notion of order, and we've got Chaos. All these values are represented by supernatural beings called gods. These gods take a rather active part in people's lives.

Now, some games do not make such assumptions. Some games actually completely ignore the whole subject. Other games introduce gods and their manipulations but choose to ignore the people's role in the axiological system. D&D embraces the subject openly and puts it in its core mechanics.
And that's it.

I just wish to address one point of criticism that is often repeated in reference to Alignment mechanics. That it pigeon-holes the individuals, players and NPC's alike. It supposedly introduces severe limitations to one's actions and moral choices.
The truth is - it does. If you're dumb as a doornail.

I admit the alignment rules explanations were ambiguous and incoherent at best, especially given the multitude of D&D editions.
But it doesn't require much of a thinker to see the sense.
Unless you're a Calvinist (God help you if you are) you should understand the basic idea of 'free will'.
A player or an NPC is free to act in any way it wills as it has the right to shape its destiny. But at any given point in time this person can be judged against the universal reference point which is the D&D axiology. At this 'judgement day' the verdict takes the form of an alignment. Thus, alignment mechanics in D&D serves two purposes. One: mechanical e.g. to determine whether a Paladin maintains its status or a the wizard's spell affects the creature. Two: as a general guideline how a particular NPC or monster could behave within reason (of course!).
No one of a sound mind should (or would) get the idea that an orc cannot be reasoned with in proper circumstances. That a villain can't cooperate with the heroes if he's got a good enough reason to do it. That a player cannot act against alignment if need be. Hey, we're not playing Munchkin D&D, there is no Lawfull Stupid or Stupid Evil alignment in the rulebook.

That said, I also have the need to point out that same rules need not apply to players and NPCs alike. While in players' case alignment is the current 'verdict' in case of DM's controlled creatures it is a compass, a quick guideline that gives him the idea of what the general character of a creature is.
But please do acknoledge that this is just a guideline, not a strict rule.
Drow are generally evil, but nothing in the world should stop you from creating a good and honorable one. Apart from thre fact that Drow have good reasons to behave the way they do. They've been cheated by Lolth for thousands of years.
Orcs are generally chaotic and evil, but they also have their reasons. They are an intelligent race yet unable to fit into the civilized world of humans, elves and dwarves. Thus, they're a common ennemy. But need not be, all depends on the circumstances.
I could go on like that forever but you should have gotten the gist by now.

Getting back to the players, my final advice for the DM is to keep alignments secret from them. They should have their idea of playing the character. You are their judge however. You decide whether the Paladin falls from grace unexpectedly. It's the game's requirement that alignments are defined at proper times. But make this a background mechanics, unseen for the players. Let them shape their destiny the way they want. Let them feel this moral anxiety. You just deliver the verdict and play out the consequences accordingly. Both sides will have fun at that this I promise.